A former Massachusetts chemist may plead guilty at a change-of-plea hearing that has been scheduled for Nov. 22, according to court documents released Monday.

A former Massachusetts chemist may plead guilty at a change-of-plea hearing that has been scheduled for Nov. 22, according to court documents released Monday.

Annie Dookhan, a chemist at the center of a Massachusetts lab scandal that has compromised thousands of drug cases, originally entered a plea of not guilty to obstruction of justice and tampering with evidence.